code: def _str_optional(s):
      return "NULL" if s is None else f"'{quote(str(s))}'"
  
file_path: mlflow/mlflow/rfunc/backend.py
imports: import logging
  import os
  import re
  import subprocess
  import sys
  from mlflow.exceptions import MlflowException
  from mlflow.models import FlavorBackend
  from mlflow.tracking.artifact_utils import _download_artifact_from_uri
  from mlflow.utils.string_utils import quote
label_desc: Use image node_id 2 for calling a global function with example usage: _str_optional(s) and returns: unknown